The present invention relates to the field of implantable prostheses. More specifically, the present invention relates to implantable prosthetic cardiac, aortic, and venous valves.
In human pathology, the proper functioning of both cardiac and venous valves is of paramount importance. Disorders of cardiac valves cause significant morbidity and mortality. These disorders affect persons of all ages and can result from congenital or degenerative conditions, as well as from the sequelae of infections. Stenosis and insufficiency of the aortic or mitral valves have a greater incidence than stenosis and insufficiency of the tricuspid and pulmonary valves. Venous insufficiency is believed to contribute to various maladies, including edema, varicose veins, aching leg pain while standing, lipodermatosclerosis, and ulcerations. Venous insufficiency is essentially caused by venous hypertension and chronic venous stasis due to valvular incompetence both of an idiopathic nature and of a secondary nature following past illnesses of the venous systems.
A prosthetic cardiac or venous valve may regulate the direction of the pulsating blood flow so as to limit the occurrence of blood stasis in the region about the valve. By maintaining the direction of blood flow therethrough, a prosthetic cardia, aortic, or venous valve may alleviate the maladies resulting from valve disorders or venous insufficiency. A prosthetic valve should therefore permit blood flow in the proper predetermined direction to limit or prevent backflow of the blood in a reverse direction.
The art has seen several attempts for providing a prosthetic valve to alleviate the consequences of cardiac valve disorders and of venous insufficiency. These attempts generally fall into two categories, biologic valves and mechanical valves. Biologic valves are comprised of a stent supporting a number of circumferential leaflets made of a flexible material. If the material is biologic in nature, it may be either a xenograft, that is, harvested from a non-human cadaver, or an allograft, that is, harvested from a human cadaver. For example, it is known in the art to apply a pericardium biological tissue layer covering, for providing the valve leaflets, to a stent which provides structural annular integrity to the prosthesis. Non-biologic material such as polyurethane has also been used. The second category of prosthetic valves, mechanical valves, usually comprise a rigid annulus supporting up to three rigid leaflets. The annulus and leaflets are frequently formed in pyrolitic carbon, a particularly hard and wear resistant form of carbon. The annulus is captured within a sewing ring so that the valve may be attached to tissue at the location of the replaced valve. Unfortunately, surgically positioning these implants typically requires suturing or sewing the device into the blood vessel, increasing the risk of thrombosis due to the resulting suturing or anastomoses of the body vessel.
These attempts typically provide a valve structure having a relatively rigid tubular body structure which supports a flexible valve leaf structure. That is, any structural rigidity imparted to the tubular body structure is separated from the valve leaf structure. For example, U.S. Pat. No. 4,759,759 discloses a prosthetic valve having a solid stent member having a diametrically-opposed upstanding posts and a substantially cylindrical flexible cover. The two portions of the cover extending between the upstanding stent posts may be collapsed against each other in sealing registry over a fluid passageway defined by the stent. The stent, being a solid member, limits the radial collapsing thereof for endoscopic delivery within a body lumen. The cover, being unsupported by the stent within the fluid passageway of the valve, must itself provide sufficient strength and resiliency to optimally regulate fluid flow. Alternatively, U.S. Pat. No. 5,855,691 discloses a prosthetic valve having a radially expandable covered stent which defines an elongate fluid passageway therethrough. A flexible valve is disposed within the fluid passageway to regulate fluid flow therethrough. The valve is formed of a flexible and compressible material formed into a disc with at least three radial incisions to form deflectable leaflets. While the stent circumferentially supports the valve body, the leaflets are not supported by any other structure within the fluid passageway. There is therefore a need in the art for a unitary prosthetic valve construction which provides structural reinforcement to both the tubular body portion of the valve and to the valve leafs supported thereon.
The present invention is directed to providing a fully prosthetic valve having valve leafs formed from a covered valve leaf frame and which may be implanted using a minimally-invasive, endoscopic technique.
The present invention provides a prosthetic valve for implantation within a body lumen. The prosthetic valve of the present invention provides a device for regulating and maintaining the direction of a pulsating fluid flow through the body lumen. The valve includes a radially-collapsible scaffold portion and a radially-collapsible leaf valve portion. The scaffold portion includes a tubular open body scaffold defining a fluid passageway therethrough. The leaf valve portion is deflectable between a closed configuration in which fluid flow through the valve passageway is restricted and an open configuration in which fluid flow through the valve passageway is permitted.
Each of the valve leafs desirably includes a valve leaf frame having an open construction so as to facilitate radially-collapsing or -expanding the leaf valve portion of the valve. Each valve leaf frame defines a valve leaf aperture with the scaffold. The present invention seals each valve leaf aperture to prevent fluid flow therethrough. The material used to seal each valve leaf aperture is sufficiently thin and pliable so as to permit radially-collapsing the leaf valve portion for delivery by catheter to a location within a body lumen. A fluid-impermeable biocompatible non-thrombogenic valve leaf cover may be positioned on each valve leaf frame so as to seal the valve leaf aperture. The valve leaf cover may be formed from a surgically-useful textile such as Dacron, polyethlylene (PE), polyethylene terephthalate (PET), silk, Rayon, or the like. The valve leaf cover may also be formed of a surgically-useful polymeric material such as urethane, polytetrafluoroethylene (PTFE) or expanded polytetrafluoroethylene (ePTFE). The valve leaf cover may also coated with a cellular growth-inhibiting drug such as Heparin or Taxol or another such composition.
Similarly, each of the valve leaf apertures may be covered with cultured tissue cells derived from a either a donor or the host patient which are attached to the valve leaf frames. The cultured tissue cells may be initially positioned to extend either partially or fully into each valve leaf aperture. In order to provide additional support to the attached cultured tissue cells, a microfilter-type support mesh spanning the valve leaf aperture may also be provided. The present invention further contemplates that the supporting scaffold and valve leaf frames may be formed of either a bioabsorbable material or a non-bioabsorbable material. It is contemplated that the scaffold and valve leaf frames which are formed from a bioabsorbable material will eventually be displaced by the tissue cells as the tissue cells mature. Eventually the cells alone will provide the fully functioning valve. Alternatively, when the scaffold and valve leaf frames are formed from a non-bioabsorbable material, the cultured cells provide a means for reducing any undesirable biological response by the host.
The leaf valve member is normally spring biased towards the closed configuration. The present invention also contemplates biasing the leaf valve member towards the open configuration to simulate known anatomical mechanics of a valve in which the leaf valve portion would close upon experiencing sufficient back flow pressure from the direction downstream from the valve.
The leaf valve portion desirably includes a number of valve leafs which are deflected between the closed and open configurations when the fluid pressure differential thereacross exceeds a predetermined threshold. That is, the fluid pressure differential acts to open the valve when the fluid pressure upstream of the valve leaf portion is greater than the fluid pressure downstream of the valve leaf portion.
Each of the valve leafs is deflectably supported by the scaffold at a flexible hinge. The present invention contemplates that the open and closed configurations of the valve may be defined either downstream or upstream of the flexible hinges. It is desired that the scaffold portion of the valve will eventually provide fluid-tight engagement with the body lumen although it is contemplated that some leaking or fluid flow between the scaffold portion and the body lumen is still acceptable. Just as it is preferred, but not required, that the valve leafs prevent fluid flow in the closed configuration, it is recognized that substantial restriction of fluid flow past the scaffold-lumen interface may still provide a prosthetic valve exhibiting acceptable performance characteristics.
The present invention shows and describes both a bicuspid valve and a six-leaf valve, although designs employing a different number of valve leafs are clearly within the scope of the present invention. The bicuspid valve includes a pair of leaf frames which deflect about a hinge positioned downstream of the closable valve opening. The six-leaf variant includes valve leafs which deflect about hinges positioned upstream of the closable valve opening.
The abutting engagement between adjacent valve leafs, while desirably providing a fluid-tight seal, is contemplated to significantly restrict backflow past the valve leafs. The abutting engagement between adjacent valve leafs may therefore provide less than complete fluid integrity while still achieving the desired performance parameters.
The scaffold of the valve includes a first end defining a first opening, a second end defining a second opening, a substantially cylindrical interior face, a substantially cylindrical exterior face, and at least one radially-extending scaffold opening communicating between interior and exterior faces. The interior face generally defines the fluid passageway. The scaffold and leaf valve member are formed to be expandable from a first diameter permitting delivery through the body lumen to a second radially-expanded diameter for retentively engaging the body lumen at a desired location. The scaffold may be formed having a shape memory favoring radial self-expansion or may be formed so as to permit radial expansion by a delivery balloon which is deflated and withdrawn after scaffold expansion against the body lumen. The scaffold may further provide at least one radially outwardly projecting hook member for retentively engaging the fluid conduit when expanded thereagainst.
The present invention also contemplates forming both the scaffold and the valve leaf frames as a unitary support trellis. The unitary trellis may be formed by a single undulating wire bent to form both the radially expandable scaffold portion and the radially expandable valve leaf frames. While various configurations for the unitary support trellis of the present invention are contemplated, one preferred configuration bends a wire along a longitudinally extending and retracting undulating path so as to alternately define a collapsible and expandable leaf frame aperture and then a collapsible and expandable scaffold aperture. The wire may be laid along a flat surface so as to form a planar trellis preform. The trellis preform may then be wrapped about an elongate cylindrical mandrel. The valve leaf frames may be deflected about their respective hinges to establish a shape memory in either the open or closed configuration either prior to or after wrapping the trellis preform about the mandrel.
The trellis is desirably formed from a biocompatible metal or polymeric material. The trellis may additionally be formed from a shape-memory material to more reliably provide the required geometry to function effectively within the valve once radially expanded at a site within a lumen. The trellis may be formed from an alloy of nickel and titanium in specific proportions known in the art as nitinol. Alternatively, the trellis may be formed from a polymeric material which allows the trellis to be radially collapsed for delivery to a site in a lumen but then radially expands to return to an undeflected shape so as to function effectively within the valve.
The present invention also contemplates attaching an elongate generally cylindrical first biocompatible non-thrombogenic liner to the trellis. The first liner may be positioned on either the interior or exterior face of the scaffold. The first liner may also provide the sealing cover for the valve leaf frame apertures. The first liner may be trimmed to span between adjacent valve leafs in the open configuration so as to provide a larger surface area for the body fluid to act upon when urging the valve leafs between the open and closed configuration. The first liner may also be trimmed to provide at least one flap extending in the downstream direction beyond each valve leaf. Each flap may then be folded over the adjacent valve leaf frame and laminated through a valve leaf aperture to the liner.
Furthermore, an elongate generally cylindrical second biocompatible non-thrombogenic liner may be positioned on the scaffold opposite the first liner. The second liner may desirably extend only along a portion of the scaffold or fully along scaffold. The first and second liners may be joined so as to fully encase either just the scaffold or the entire trellis. It is contemplated that the first and second liners may be laminated together through one or more openings defined by the trellis. Additionally, the second liner may be formed by folding the first liner over the first end of the scaffold so as to extend at least partially along the opposite face of the scaffold as the first lining.
Each liner positioned on the trellis may inhibit thrombus formation and facilitate tissue ingrowth therethrough for assimilating the valve of the present invention into the body lumen. Towards this latter goal, one or both of the liners may be formed from a porous textile or polymeric material. It is further contemplated that either liner may be formed from an xenograft of cellular tissue from a donor such as bovine cardial tissue, or homograft of cellular tissue formed from the host patient.
It is also contemplated by the present invention that the prosthetic valve may also be attached to the interior surface of a second radially collapsible prosthetic fluid conduit. The second fluid conduit may be selected from many known stent and covered stent designs known in the art. The second fluid conduit further maintains the patency of the lumen to either side of the valve and may also include a biocompatible fluid impermeable non-thrombogenic lining on either or both of its own inner or outer surfaces. The materials used to form the second fluid conduit may also be selected to be either bioabsorbable or non-bioabsorbable as may be desired.
The present invention is also directed to methods of making the prosthetic valve of the present invention.